Nitrogen-doped Carbon Polyhedrons Research Articles

Integrating CoP/Co heterojunction into nitrogen-doped carbon polyhedrons as electrocatalysts to promote polysulfides conversion in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have garnered extensive research interest as one of the most promising energy storage devices due to their ultra-high theoretical energy density. However, the sluggish reaction kinetics, abominable shuttling effect and inferior cycling stability severely restrict its practical application. Herein, a multifunctional CoP/Co@NC/CNT heterostructure host material was elaborately designed and synthesized by integrating CoP/Co heterojunction, N-doped carbon hollow polyhedrons (NC) and carbon nanotubes (CNTs). Specifically, the CoP/Co heterojunction can reconfigure the local electronic structure, resulting in a synergistic effect that enhances adsorption capacity and catalytic activity compared to CoP and Co alone. Furthermore, the CNTs-grafted NC not only provides multi-dimensional pathways for rapid electron transport and ion diffusion, but also physically restricts the diffusion of polysulfides during charge-discharge processes. Owing to these advantages, the battery assembled with the CoP/Co@NC/CNT/S cathode yields an impressive discharge specific capacity of 1479.9 mAh g−1 at 0.1C, and excellent capacity retention of 793.7 mAh g−1 over 500 cycles at 2C (∼85.5 % of initial capacity). The rational integration of multifunctional heterostructures could provide an effective strategy for designing high-efficiency nanocomposite electrocatalysts to promote sulfur redox kinetics in Li-S batteries.

Sterical Self-Consistency of Carbonaceous Nanopolyhedra Triggered by Introduced CNTs to Optimize ORR Performance

The electrocatalyst of oxygen reduction reactions is one of the basic components of a fuel cell. In addition to costly Pt/C benchmark catalysts, cost-effective carbon-based catalysts have received the most attention. Enormous efforts have been dedicated to trade off the catalyst performance against the economic benefit. Optimizing composition and/or structure is a universal strategy for improving performance, but it is typically limited by tedious synthesis steps. Herein, we have found that directly introducing CNT into MOF-derived carbonaceous nanopolyhedra, i.e., introduced carbon nanotubes (CNTs) penetrated porous nitrogen-doped carbon polyhedra (NCP) dotted with cobalt nanoparticles (denoted as CNTs-Co@NCP), can optimize the catalytic activity, stability, and methanol tolerance. The hierarchical architecture combines the 0D/1D/3D Co/CNT/NCP interfaces and 1D/3D CNT/NCP junctions with the frameworks with a greatly exposed active surface, strengthened mass transport kinetics, stereoscopic electrical conductivity networks and structural robustness. The sterical self-consistency of MOF-self-assembly triggered by introduced CNTs demonstrates tactful ORR electrocatalytic activity regulation. Eventually, the CNTs-Co@NCP showed a half-wave potential (E1/2) of 0.86 V and a diffusion-limited current density (JL) of 5.94 mA/cm2 in alkaline electrolyte. The CNTs-Co@NCP was integrated into the cathode of a direct methanol fuel cell (DMFC) with an anion-exchange membrane, and an open-circuit voltage (OCV) of 0.93 V and a high power density of 46.6 mW cm−2 were achieved. This work successfully developed a catalyst with competitive ORR performance through plain parameter fine-tuning without complex material design.

Unveiling the efficient sodium storage and mechanism of MOFs-induced CoSe@N-doped carbon polyhedrons decorated with 2H-MoSe2 nanosheets

Hybrid hierarchical nanostructures have a significant impact on engineering novel anode materials for boosting the performance of sodium-ion batteries (SIBs). Here, a hierarchical porous structure constituted by CoSe nanocrystals embedded in nitrogen-doped carbon polyhedron with the embellishment of 2H-MoSe2 nanosheets (CoSe@NC/MoSe2) is fabricated by a metal-organic frameworks (MOFs)-engaged strategy and subsequent selenization reaction. The presence of N-doped carbon matrix and bimetallic selenides significantly enhance electronic and ionic diffusion kinetics. In addition, the porous structure provides short Na+ diffusion distance and guarantees outstanding structural stability upon cycling. Due to these distinctive features, the CoSe@NC/MoSe2 composite displays superior cyclability of 305.9 mAh g−1 up to 1500 loops at 5.0 A g−1 and exceptional rate property of 286.1 mAh g−1 at 10.0 A g−1 for sodium storage. When matched with Na3V2(PO4)3@C cathode, a SIB full cell can maintain a high invertible capacity of 78.9 mAh g−1total over 100 loops at 0.5 A g−1. Moreover, the multistep conversion reactions mechanism is further identified by kinetics analysis, and ex situ and in situ characterization.

1D/3D rambutan-like Mott–Schottky porous carbon polyhedrons for efficient tri-iodide reduction and hydrogen evolution reaction

Realizing rapid electron transfer and mass diffusion in virtue of interface regulation and nanostructure design is an effective strategy to augment the catalytic activity of carbon materials but still a significant challenge. Herein, a novel frontier 1D/3D rambutan-like Mott-Schottky-type nitrogen-doped carbon polyhedron (NiCo-NCP/CNT) consisting of nickel/cobalt species and a 3D porous carbon skeleton intertwined with 1D carbon nanotubes (CNT) is controllably fabricated by rationally utilizing Co/Zn bimetallic-organic frameworks and nickel ions. The photovoltaic device fabricated with NiCo-NCP/CNT electrocatalyst achieves a power conversion efficiency of 8.75%, which is superior to that of conventional Pt electrodes (7.25%). When the NiCo-NCP/CNT electrocatalyst is employed as the cathode for water splitting under alkaline conditions, an overpotential as low as 63 mV is demonstrated at a current density of 10 mA·cm−2. The improved work function (from 4.65 to 4.59 eV) proves that introducing NiCo favors regulating electronic states and optimizing energy level, which could induce more robust self-driven electron transfer at the Mott-Schottky interface. The proposed nickel adsorption-sintering strategy effectively promotes electron/mass transfer capability simultaneously in carbon-based Mott-Schottky catalysts and paves the way for developing low-cost and high-performance electrocatalysts in electrocatalytic fields.

High energy density lithium-ion capacitor enabled by nitrogen-doped amorphous carbon linked hierarchically porous Co3O4 nanofibers anode and porous carbon polyhedron cathode

Lithium-ion capacitors (LICs) are emerging as progressive energy storage systems with high energy density, high power output, and a long cycle life span. The key to constructing LICs with high performances is alleviating the dynamics mismatch between the faradic anode and capacitor-type cathode. Herein, nitrogen-doped amorphous carbon linked hierarchically porous Co 3 O 4 nanofibers (NAC- l -Co 3 O 4 NFs) were prepared by electrospinning strategy, where the amorphous carbon can mitigation the volume variation of Co 3 O 4 during the lithiation/delithiation process, while the hierarchically porous structure provides effective channels and exposes more active sites for fast electron transfer and Li + storage. The delicate structure endows NAC- l -Co 3 O 4 NFs with remarkable rate capacity and robust cycling durability. Furthermore, nitrogen-doped carbon polyhedron (NPCP) is prepared for the cathode, displaying superior rate performances and cycling stability. As a result, by assembling the NAC- l -Co 3 O 4 //NPCP LICs, a high energy density of 296 Wh kg −1 and a high output of 11750 W kg −1 is delivered. Additionally, the LIC devices display excellent cycle lifespan (80% capacity retention after 10000 cycles at 1 A g −1 ). • Nitrogen-doped amorphous carbon-linked Co 3 O 4 1D nanostructured anode (NAC-l-Co 3 O 4 NFs) is fabricated via electrospinning technique. • The 1D nanofibers interlink into a 3D network further facilitating ions/electrons transmittability. • The LIC assembled with NAC- l -Co 3 O 4 anode shows an ultrahigh energy density (357 Wh kg) and excellent cycling stability.

Nitrogen-Doped Carbon Polyhedrons Confined Fe-P Nanocrystals as High-Efficiency Bifunctional Catalysts for Aqueous Zn-CO2 Batteries.

Emerging Fe bonded with heteroatom P in carbon matrix (FePC) holds great promise for electrochemical catalysis, but the design of highly active and cost-efficient FePC structure for the electrocatalytic CO2 reduction reaction (CO2 RR) and aqueous ZnCO2 batteries (ZCBs) is still challenging. Herein, polyhedron-shaped bifunctional electrocatalysts, FeP nanocrystals anchored in N-doped carbon polyhedrons (Fe-P@NCPs), toward a reversible aqueous ZnCO2 battery, are reported. The Fe-P@NCPs are synthesized through a facile strategy by using self-templated zeolitic imidazolate frameworks (ZIFs), followed by an in situ high-temperature calcination. The resultant catalysts exhibit aqueous CO2 RR activity with a CO Faradaic efficiency up to 95% at -0.55V versus reversible hydrogen electrode (RHE), comparable to the previously best-reported values of FeNC structure. The as-constructed ZCBs with designed Fe-P@NCPs cathode, show the peak power density of 0.85mW cm-2 and energy density of 231.8Wh kg-1 with a cycling durability over 500 cycles, and outstanding stability in terms of discharge voltage for 7 days. The high selectivity and efficiency of the battery are attributed to the presence of highly catalytic FeP nanocrystals in N-doped carbon matrix, which can effectively increase the number of catalytically active sites and interfacial charge-transfer conductivity, thereby improving the CO2 RR activity.

Single Cobalt Atoms Decorated N-doped Carbon Polyhedron Enabled Dendrite-Free Sodium Metal Anode.

Uncontrollable growth of sodium dendrites during the sodium deposition and stripping processes remains a huge challenge for achieving high-performance sodium metal batteries (SMBs), which results in ineffective utilization of metallic Na, low Coulombic efficiency, and inferior cycling life. Here, a single Co atom uniformly decorated porous nitrogen-doped carbon polyhedron (CoSA @NC) matrix has been fabricated and introduced to control the Na growth and achieve uniform Na nucleation/deposition. Cryo-electron microscopy and in situ optical microscopy techniques have been utilized to analyze the morphology change of metallic Na during plating/stripping processes. The single Co atoms evenly embedded in NC electrodes can provide stable Na-philic sites for Na ions adsorption, which is helpful to guide the uniform sodium deposition and prevent Na dendrites growth. This work thus provides an effective solution to inhibit Na dendrite growth and control Na nucleation behavior from the perspective of atomic level, towards the fabrication of high-safety and long-cycling SMBs.

Engineering interfacial coupling between Mo2C nanosheets and Co@NC polyhedron for boosting electrocatalytic water splitting and zinc-air batteries

The cost-effective and durable electrocatalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is vital to overall water splitting and regenerative metal-air batteries. Herein, we presented a simple metal-organic framework (MOF)-based approach for facile fabrication of noble-metal-free trifunctional heterostructure electrocatalysts. Different from traditional MOF-derived composite materials, Mo2C nanosheets are vertically aligned on the surface of cobalt-embedded nitrogen-doped carbon polyhedron (Mo2C/Co@NC). Benefiting from the reciprocally permeated structure and strong interfacial coupling effects between Mo2C nanosheets and Co@NC polyhedron, the intrinsic activities and the accessible active sites toward HER, OER and ORR are significantly improved, which endows Mo2C/Co@NC with high electrocatalytic activity and durability as a trifunctional electrocatalyst. Notably, Mo2C/Co@NC-based Zn-air battery could efficiently power the electrochemical water splitting using Mo2C/Co@NC as the electrodes. This work provides one heterostructural protocol to construct new types of noble-metal-free trifunctional electrocatalysts for boosting water splitting and zinc-air batteries.

Unique Nitrogen-Doped Carbon Polyhedron Embedded with Co Derived Core-Shell Nanoparticles for the Electro-Catalysis towards Hydrogen Peroxide Redox Reaction and Nonenzymatic Detection

Unique nitrogen-doped carbon polyhedron embedded with core–shell Co@Co3O4 nanoparticles (Co@Co3O4-NC) was synthesized with the pyrolysis of zeolitic imidazolate framework. Novel two-step redox pyrolysis with accurate control of ZIF-67 carbonization and Co ion transformation during pyrolysis was applied. Co@Co3O4-NC was characterized by field emission scanning electron microscope, high-resolution transmission electron microscope, powder X-ray diffraction, X-ray photoelectron spectroscopy and nitrogen adsorption-desorption experiment. Co@Co3O4-NC displayed a strong electrochemical catalysis towards both H2O2 oxidation and H2O2 reduction. By using Co@Co3O4-NC prepared sensor, efficient detection of H2O2 was achieved not only by the H2O2 oxidation at a positive potential but also by the H2O2 reduction at a negative potential. At 0.30 V, the resulting sensor exhibited a rapid amperometric response (2 s), low detection limit (0.056 μM) and broad detection linear range (0.1 μM–40.0 mM). Besides, at −0.30 V, the resulting sensor also exhibited a rapid amperometric response (4 s), low detection limit (0.96 μM) and broad detection linear range (2.0 μM–60.0 mM). Additionally, Co@Co3O4-NC prepared sensor also presented a notable selectivity, high reproducibility and long-term stability. Our results proved that Co@Co3O4-NC was an efficient electro-catalyst for H2O2 redox reaction, and Co@Co3O4-NC prepared sensor could be a promising sensing platform for the nonenzymatic detection of H2O2.

Enhancing potassium-ion battery performance by MoS2 coated nitrogen-doped hollow carbon matrix

As an important alternative to lithium-ion batteries (LIBs), potassium-ion batteries (PIBs) have attracted much attention due to the abundance and low cost of potassium, however, it is still a great challenge to select suitable anode materials to accommodate the large-size of K-ion. Herein, MoS2 nanosheets were coated on the porous carbon polyhedron derived from zeolite imidazole framework-8 (designated as PCP@MoS2) and employed as the anode materials for PIBs. Benefiting from the high electrical conductivity, strong structure stability of the nitrogen-doped carbon polyhedron and the layered crystal structure of MoS2, the reversible capacity can be maintained at 375 mA h g−1 after 100 cycles at 100 mA g−1, 200 mA h g−1 after 200 cycles at 500 mA g−1 as well as excellent rate property. The excellent electrochemical performance can be attributed to the unique hybrid structures and the synergistic effects between MoS2 and N doped porous carbon polyhedron, which could enhance the electronic conductivity, shorten the K-ion diffusion distance, mitigate the agglomeration of the MoS2 nanosheets, relieve the volume variation, and provide plenty of active sites for K ion accomodation.

Nano-engineered directed growth of Mn3O4 quasi-nanocubes on N-doped polyhedrons: Efficient electrocatalyst for oxygen reduction reaction

Engineering the morphology of integral building blocks is a key step in broadening their catalytic activities. In this work, an interesting structure is reported by oriented and directed growth of manganese oxide (Mn3O4) quasi-nanocubes on nitrogen doped mesoporous carbon polyhedrons resulting from zeolite imidazole framework (ZIF-8). The prepared Mn3O4/NCP (Mn3O4 quasi-nanocubes on the surface of N-doped carbon polyhedrons) hybrid catalyst showed activity and durability comparable to Pt/C and higher than nitrogen-doped carbon polyhedrons (NCP) and pure Mn3O4. Further studies indicate that oxygen reduction reaction (ORR) is carried out via a four electron transfer mechanism with very low production of hydrogen peroxide (3%). In this perspective, Mn3O4/NCP is an auspicious nominee as a cathodic catalyst because of inexpensive Mn and good durability. Our synthetic strategy may open a new avenue for material synthesis.

Correction: In situ encapsulation of core–shell-structured Co@Co3O4 into nitrogen-doped carbon polyhedra as a bifunctional catalyst for rechargeable Zn–air batteries

Correction for ‘In situ encapsulation of core–shell-structured Co@Co3O4 into nitrogen-doped carbon polyhedra as a bifunctional catalyst for rechargeable Zn–air batteries’ by Ziyang Guo et al., J. Mater. Chem. A, 2018, 6, 1443–1453, DOI: 10.1039/C7TA09958D.

In-situ embedding MOFs-derived copper sulfide polyhedrons in carbon nanotube networks for hybrid supercapacitor with superior energy density

The binder-free flexible electrode materials have greatly potential for portable flexible new energy equipment. Herein, we rationally fabricate a flexible composite electrode by connecting the HKUST-1 derived copper sulfide (CuS) polyhedrons with carbon nanotubes (CNT). Because of the synergistic interaction of the HKUST-1 derived CuS polyhedrons and the CNTs network, many excellent electrochemical properties of the composite thin film are obtained working as supercapacitors electrodes. The specific capacitance of the as-prepared electrode can achieve 606.7 F g−1 at a current density of 1 A g−1. Moreover, the as-fabricated asymmetric supercapacitors by using HKUST-1 derived CuS polyhedrons and nitrogen-doped carbon polyhedrons interspersed into carbon nanotubes films act as positive (CCS) and negative (CNC) electrodes deliver up to a higher energy density of 38.4 W h kg−1 at a power density of 750 W kg−1, which also show a favourable cycle life (87.0% capacity retention after 6000 cycles). It indicates that the electrodes we fabricated are potential electrode materials and our research offers a valuable inspiration for high performance energy storage devices.

Template-Directed Bifunctional Dodecahedral CoP/CN@MoS2 Electrocatalyst for High Efficient Water Splitting.

Designing high efficient and noble metal-free bifunctional electrocatalysts for both hydrogen and oxygen generation is still critical and challenged. In this study, hierarchical dodecahedral-structured CoP/CN@MoS2 is prepared through a two-step calcination treatment and a solvothermal approach. The metal-organic framework of ZIF-67 is chosen to serve as the template and for providing Co sources, in which ZIF-67 is first transformed to Co nanoparticles embedded in nitrogen-doped carbon polyhedrons and then transformed to CoP/CN. MoS2 nanosheets are further grown on the surface of dodecahedral-structured CoP/CN with a solvothermal method. Benefiting from the synergistic coupling effect of CoP and MoS2 and the nitrogen-doped carbon matrix, advanced hydrogen evolution reaction (HER) both in acid and alkaline solution as well as splendid oxygen evolution reaction (OER) performance in alkaline aqueous were achieved. Moreover, the coupling effect of CoP/CN and MoS2 is disclosed theoretically by density functional theory calculations to validate the increased HER activity. The as-prepared hybrid CoP/CN@MoS2 not only exhibits decent HER activity in acidic (η10 = 144 mV) and alkaline solutions (η10 = 149 mV), but also exhibits splendid OER activity (η10 = 289 mV) in 1.0 M KOH. This work represents a solid step toward boosting the electrocatalytic kinetics of nonprecious catalysts.

Enhancing Li-S redox kinetics by fabrication of a three dimensional Co/CoP@nitrogen-doped carbon electrocatalyst

The design of sulfur hosts with high electrochemical activity and high sulfur loading plays a vital role in developing high-energy-density lithium-sulfur batteries. Herein, a novel type of sulfur cathode substrate is established via a facile two-step process, in which the Co and CoP nanoparticles are embedded in a three-dimensional (3D) porous nitrogen-doped carbon polyhedron (Co/CoP@NC). These Co and CoP nanograins not only act as polysulfides capturing centers but also the electrocatalysts effectively promoting the redox kinetics towards polysulfides conversion, as confirmed by the experimental results and DFT calculations. Meanwhile, the interconnected 3D porous N-doped carbon architecture contributed to Li+ transportation, electrolyte infiltration and relieves volume expansion of sulfur. Thus, Li-S batteries configured with the S@Co/CoP@NC cathode exhibit a remarkable enhancement in the rate capability and cycling performances. When sulfur content is controlled to be 75.8 wt%, the S@Co/CoP@NC cathode delivers an outstanding high-rate capability up to 30 C and low capacity decay rates of 0.033% and 0.03% per cycle over 1000 cycles at 1 C and 2 C, respectively.

In situ grown α-Cos/Co heterostructures on nitrogen doped carbon polyhedra enabling the trapping and reaction-intensification of polysulfides towards high performance lithium sulfur batteries.

Lithium sulfur (Li-S) batteries are considered as one of the most promising next generation energy storage systems, whereas their intrinsic drawbacks impeded their practical implementation. Herein, a nitrogen doped porous carbon polyhedron coupled with a well distributed α-CoS/Co heterostructure mediator was designed and prepared as the sulfur cathode host for lithium sulfur batteries. The α-CoS/Co heterostructure on a nitrogen doped carbon polyhedron (NCP) not only provides a strong adsorption interaction towards soluble polysulfides, but more importantly, also promotes the fast conversion of polysulfides to insoluble products, chemically suppressing the shuttling of polysulfides through the simultaneous advantages of α-CoS and Co. As a result, the α-CoS/Co-NCP-S cathode exhibits high sulfur utilization with a 1611.4 mA h g-1 first discharge capacity and a well satisfactory redox cycling stability with a low capacity fade rate of 0.042% per cycle at 0.5 C for over 800 cycles. Moreover, the hybrid cathode delivers 860.2 mA h g-1 specific capacity for a high sulfur loading of 4.8 mg cm-2 with remarkable cycling performance.

Energy level engineering in transition-metal doped spinel-structured nanosheets for efficient overall water splitting

A series of hollow polyhedrons are constructed with transition-metal doped spinel-structured nanosheets wrapped nitrogen-doped carbon polyhedrons for enhanced water splitting.

Hierarchical Nanospheres Constructed by Ultrathin MoS2 Nanosheets Braced on Nitrogen-Doped Carbon Polyhedra for Efficient Lithium and Sodium Storage.

MoS2 has attracted a lot of attention for electrochemical energy storage. Herein, we design and fabricate unusual hierarchical composite nanospheres by cultivating a MoS2 sheet-like nanostructure on nitrogen-doped carbon polyhedra (designated as CP@MoS2 nanospheres). The nitrogen-doped carbon polyhedra are able to significantly boost the electrical conductivity of the hybrid architecture and largely mitigate the agglomeration of the MoS2 nanostructure. The sheet-like MoS2 nanostructure can render a great deal of storage sites toward lithium and sodium. When measured as a negative electrode for Li storage, these CP@MoS2 nanospheres manifest a large charge capacity of approximately 549 mAh g-1, a superior cycle life of 900 cycles, and excellent rate property. Furthermore, they also demonstrate improved electrochemical activity for Na+ ion storage.

MOF derived nitrogen-doped carbon polyhedrons decorated on graphitic carbon nitride sheets with enhanced electrochemical capacitive energy storage performance

Three dimensional carbon materials with hirerarchically porous structure could exhibit superior energy storage performance than two dimensional stacked carbon nanosheet materials. In this work, we prepared a novel ZIF-8-derived nitrogen doped carbon nanoparticles/graphitic carbon nitride composite electrode material with high electrochemical energy storage performances, including high specific capacitances (495 F g−1 at 0.1 A g−1 and 188 F g−1 at 20 A g−1) and a stable cycling durability with no capacitance declination after 5000 charge-discharge cycles in three-electrode system. When assembled as electrode materials in symmetrical two-electrode system, the as-prepared composite electrode material could exhibit high specific capacitances of 349.7 F g−1 at 0.5 A g−1 and 261.2 F g−1 at 5 A g−1. Accordingly, a high energy density of 11.89 Wh/kg can be achieved at the power density of 247.40 W kg−1. The improvement stems from its hierarchically porous structure with dominant pore sizes at 3 nm and among 4–40 nm, as well as high exposed pyridinic nitrogen (8.58 at%) and pyrrolic nitrogen (3.59 at%) active sites caused by the insertion of ZIF-8-derived nitrogen doped carbon nanoparticles between g-CN layers. This study has provided a new idea on the design of graphitic carbon nitride nanostructures with improved doping level and hiearchically porous structure.

In situ encapsulation of core–shell-structured Co@Co3O4 into nitrogen-doped carbon polyhedra as a bifunctional catalyst for rechargeable Zn–air batteries

Co@Co3O4@NC-900 is designed and used as a catalyst for bulk and flexible Zn–air batteries which display good electrochemical performance.